The present invention relates to motor-vehicle automatic transmissions with multi-stage gear ratios. More precisely, it relates to a fuzzy-logic process for control of gear ratios by disabling and enabling, which process permits improvement of vehicle driving comfort and safety, regardless of the driving or traveling conditions encountered (uphill, downhill or level).
In most currently used methods for control of gear ratio changes in automatic mode, the gear ratio changes are actually authorized as a function of vehicle speed and engine load. Most often, these speed and load criteria are translated in the form of gear ratio change laws, which are conveniently visualized in a graph having coordinates of Vveh/xcex1pap, where Vveh denotes the vehicle speed and xcex1pap the gas throttle opening angle, or more generally the percentage opening of the device for regulation of admission of fuel to the engine.
An example of a commonly used gear ratio shift law is proposed in FIG. 1, in which curve 1 represents the downshift curve (or in other words a decrease from ratio N to ratio Nxe2x88x921, abbreviated as N/Nxe2x88x921), and curve 2 represents the upshift curve (abbreviated N/N+1), where N is the current gear ratio of the automatic transmission. These shift laws are defined such that the vehicle speeds at which gear ratio changes take place slide to higher values as the engine load becomes greater.
Moreover, for a given engine load, or more exactly for a given opening xcex1pap, on the other hand, the Nxe2x88x921/N shift, or in other words the shift from a lower gear ratio to the next higher gear ratio, also takes place without exception at a speed substantially higher than that at which there occurs the corresponding inverse N/Nxe2x88x921 shift, or downshift. This provision, which can be regarded as a hysteresis effect, has the purpose of avoiding an unacceptable hunting tendency between the Nxe2x88x921 and N gear ratios which would inevitably occur if the upshifts and downshifts were to take place under the same speed and load condition.
Taking as example a vehicle in acceleration while in gear ratio N with a substantially constant accelerator position xcex1pap, this phase is represented by the segment of FIG. 1 oriented along OA. It is now supposed that the driver is forced suddenly to raise his foot from the accelerator at point A. This maneuver is reflected on the same FIG. 1 by the line segment AB, which is substantially vertically oriented if the release of the accelerator is sufficiently rapid that the vehicle speed does not have time to decrease. Segment AB will intersect curve 2 at point C on FIG. 1, and the transmission then decides to shift automatically to the higher gear ratio N+1. In most cases this gear ratio change is entirely premature, and is not desired by the driver, since the engine brake of the vehicle is reduced by the shift to ratio N+1, while the driver has explicitly shown his intention to slow down by rapidly lifting his foot. As a result, this gear ratio change detracts from driving comfort, causes a feeling of not having any engine brake, and can sometimes distract the driver, thus having an influence on safety.
A satisfactory solution has nevertheless already been proposed and described in French Patent Application FR 83-07277 of May 2, 1983. It comprises associating with the gear ratio upshift and downshift curves two other curves: a negative acceleration curve and an increasing opening curve.
Thus, according to this known method, the shift to higher gear ratio is authorized only if the opening value xcex1pap is stabilized. The gear ratio is disabled when the operating point in the graph of xcex1pap versus speed is below the negative acceleration curve. It is then enabled when the operating point passes above the increasing opening curve (situated slightly above the negative acceleration curve).
This known method has several disadvantages, including the following in particular:
firstly, it is suitable only if the vehicle is not loaded and is running on the level. In fact, the negative acceleration curve is defined for these specific traveling conditions;
furthermore, it necessitates numerous calibration parameters (about 60), thus making its use difficult;
in addition, the hysteresis between the negative acceleration and increasing opening curves must remain slight to ensure that the principle can operate, but it generates gear ratio enablings which take place too soon from the viewpoint of driving pleasure;
finally, this method cannot be adapted to the driver""s driving style.
The object of the invention is therefore to provide a process for disabling and enabling ratios of the gearbox of a vehicle equipped with an automatic transmission with multi-stage gear ratios, which process permits disabling the gear ratio of the transmission (and also enabling this same ratio) effectively, regardless of the traveling conditions. Another object of the invention is to overcome the practical problems inherent in the method described in the said French Patent Application 83-07277.
To this end, the invention relates to a process for disabling and enabling gear ratios of a vehicle equipped with an automatic gearbox, characterized in that it is provided with a combination of functions (F1, F2, F3) comprising:
F1: disabling the shift of a transmission gear ratio during a first time delay, referred to as waiting time delay (Ta);
F2: disabling the shift of a gear ratio in response to instability of the fuel-supply throttle opening angle (xcex1pap)
F3: disabling the shift of a gear ratio in response to vehicle deceleration.
More precisely, the process according to the invention is provided with the stages comprising:
a) at the intersection with a curve of shift to higher gear ratio from N to (N+1), starting a first time delay known as waiting time delay Ta during which the higher gear ratio (N+1) is disabled;
b) during this time delay Ta, performing a fuzzy logic analysis of the stability of the foot; (this comprises determining a variable, referred to as UP-DEL-GRD, representative of the stability of opening of the device for regulation of admission of fuel to the engine. If this parameter is judged to be stable, then the higher gear ratio will be authorized, at the end of time delay Ta, provided the deceleration of the vehicle is not negative, in which case F3 would then be activated. In the opposite case (if the driver raises his foot rapidly, for example), a second time delay Tunstable is started, during which the higher gear ratio is still disabled. This time delay Tunstable may depend on the rate of change of xcex1pap while the foot is being raised, or else on a factor representative of the sportiness of the driving of the driver. A procedure for reinitialization and disabling of this second time delay Tunstable is also defined.
c) During this time delay Tunstable, observation of the vehicle deceleration is performed. It is also achieved in fuzzy logic from the signals xcex1pap (opening of the engine throttle) and xcex3veh, which is the real acceleration of the vehicle calculated from the vehicle speed Vveh by differentiation and filtering. The deceleration condition of the vehicle is identified by determination of a representative variable called UP-DEL-AC. When the vehicle is in deceleration phase, a phase of disabling of the higher gear ratio known as xe2x80x9cdecelerationxe2x80x9d is entered, which phase can be relatively long and which can be assimilated with the concept of xe2x80x9cnegative acceleration curvexe2x80x9d, but which is constructed from the real acceleration xcex3veh of the vehicle, thus ensuring good operation for all traveling situations (uphill, downhill or level).
Otherwise, if the vehicle does not enter the deceleration phase (the vehicle continues to accelerate), the higher gear ratio will be authorized at the end of time delay Tunstable.
d) Once the vehicle has entered the deceleration phase, the vehicle deceleration condition is continually observed. The gear ratio remains disabled as long as the vehicle acceleration remains negative. As soon as the vehicle acceleration is judged sufficient (at a certain predetermined level), the distance traveled by the vehicle is calculated from the vehicle speed. Enabling of the gear ratio is then authorized either:
when the vehicle has traveled a certain distance with xcex1pap having remained stable, or.
when the engine rpm becomes too high, or
when the downshift curve N/Nxe2x88x921 is intersected.
Exit from disabling after a certain distance has been traveled has the advantage of not enabling the ratio too rapidly, which was a shortcoming of the method described in French Patent Application FR 83-07277. In fact, when the driver while moving at moderate speed, for example in third gear, rapidly raises the accelerator upon entering a curve, this gear ratio will be disabled. The present invention will ensure that this same gear ratio will remain: disabled for a good portion of the curve, corresponding to the time that the vehicle could travel a certain distance, in contrast to the method of French Patent Application FR 83-07277, which allows enabling as soon as the decreasing opening curve is intersected.
The invention also relates to a transmission and to a motor vehicle using the process having the above characteristics for disabling and enabling gear ratios.